This specification relates to projection display technologies.
Projection display technologies display an image by projecting light corresponding to color channels of the image. A commonly used projection device is a micro-mirror display device that displays the pixels of an image by tilting micro-mirrors to project light to the display (to display the pixel) or to deflect light away from the display (to not display the pixel). The mirrors are tilted using digital control signals derived from bit plane data for the image according to a pulse width modulation scheme. The amount of time that the mirrors are turned on and off controls the intensity for a given pixel and a given color. Traditional micro-mirror displays are color sequential, that is, they project light corresponding to the color channels of an image (e.g., red, green, blue) in sequence. For example, the micro-mirror display device can adjust the mirrors for each bit of data for the red channel and project red light, then adjust the mirrors for each bit of the green channel and project green light, and then adjust the mirrors for each bit of the blue channel and project blue light.
Traditional micro-mirror displays and other projection devices can have artifacts such as color break-up, motion contour, static contour, and jitter. Color break-up occurs most commonly in areas of high contrast in an image, for example, the borders between dark and light areas of the image. When a viewer moves his or her eyes rapidly from left to right across a display screen, or when the areas of light and dark move on the display screen, a viewer may observe a rainbow shadow in the image. This rainbow is a result of the way that the viewer's retina processes the individual bursts of red, green, and blue light.
Motion contour occurs most commonly when objects having a gradual gradation in color (for example, a human face), move against the background of the image, or when a viewer's eye moves across a screen displaying objects having a gradual gradation in color. The motion on the screen can cause a viewer to observe non-existent darker or brighter shadows in the image. The shadows result from the patterns of light produced according to the pulse width modulation scheme.
Static contour occurs when the pixel data for the pixels in the image does not have sufficient bit width (i.e., does not include enough bits) to represent all of the colors in a gradation of colors in the image. When this occurs, the viewer sees edges in the image in places where there should not be edges. Traditional systems decrease static contour by applying a sequence of dither patterns to a sequence of frames of the image. However, jitter can occur when the dither pattern applied to the pixels of an image is noticeable, for example, because the dithering speed is not fast enough given the response time of the screen, or because of visible differences in the intensity values of one or more pixels being dithered. Increasing the dither bit width and the number of frames over which a sequence of patterns is applied reduces static contour, but increases jitter.